There is a lot of data in the report by Lean In and McKinsey & Company, Women in the Workplace 2015. The numbers support some beliefs, and challenge some myths, about why women remain underrepresented at the executive level of American business.

Many believe that women are underrepresented at the top because they drop off the corporate ladder. The study shows that, in fact, women leave at most levels at a lower rate than men. But they advance from one level to the next more slowly than men. Many continue to believe that women generally do not aspire to top positions. The study shows that women at every level desire to be top executives, but at a lower rate than their male counterparts. (The gap gets larger toward the top.)

One reason, the study shows, that fewer women reach the top is that they serve more often in staff vs. line positions, which are more likely to lead to the C-suite. Women in line positions are less likely to advance to the top. And women express greater concern about the stress that comes with top jobs.

And what about gender bias? The report concludes that women are more likely than men to perceive gender bias – to feel there are more barriers to promotion. Of course they do. The real question is how much gender bias exists, not what women perceive. Gender bias is hard to measure, because it is invisible and mostly unconscious. But it is certainly a factor – on its own and as an underlying part of these other phenomena. One of the recommendations of the study is training to “interrupt gender bias,” including to assure men can see and understand the challenges women encounter.

The study concludes with a “gender bias primer” from LeanIn.Org. It identifies forms of bias that parallel the unconscious mindsets I write and speak about. What I call the “double bind,” they refer to as “likeability bias”: A woman can be seen as competent or nice, but not both. What I label “unconscious images,” they include in “performance evaluation bias.” This is differences in the perceived performance of men and women, which explains why women are hired and promoted based on accomplishments “while men are hired and promoted based on their potential.” (Part of this phenomenon is what I call the “comfort principle.”)

Lean In names another, “performance attribution bias,” which is about how women are less prone to claim (and so get) credit for successes. The article points out the downward spiral that can come from this tendency: ”Because women receive less credit – and give themselves less credit – their confidence often erodes and they are less likely to put themselves forward for promotions and stretch assignments.” And they identify “maternal bias,” the assumption that mothers (and sometimes fathers) are less committed and so may be held to higher standards.

By exposing and reducing what gender bias there is, we can remove one of many factors holding women back. Until we all, men and women, become aware of the unconscious ways of thinking (our biases), the workplace will not get the full benefits of gender (or any other kind of) diversity.